Small-Medium Enterprises (SMEs) as well as other organizations (e.g. large corporations, government agencies, etc,) continuously use communication networks to enable remote branches and/or offices to access both an enterprise data center, typically located at the enterprise's headquarters (HQ), and the Internet. Accessing the enterprise data center may be required for example for intranet data processing, accessing central servers of various types (e.g. file storage facilities, electronic mail servers, etc), performing management tasks, conducting conference calls or video sessions within the enterprise or using Enterprise Resource Planning/Customer Relationship Management (ERP/CRM) systems or any other enterprise unique applications. Access to the Internet may be required since the Internet is a major source for information and data and provides connectivity on a global scale for numerous applications, such as access to web content, electronic mail exchange, etc. In some cases, connectivity to a wide area network (WAN) other than the Internet via the enterprise's head office (HO) may also be required, either instead of connectivity to the Internet or in addition to such, for example in order to provide services which might not be available at the enterprise HQ but may be available at the HO.
FIG. 1a illustrates a hierarchical topology of an enterprise network 100, comprising a plurality of small networks (120, 130 and 140) and a corporate head office (HO 101). A small network, such as small network 120, may comprise a headquarters (HQ 121), which may act as a data center and host central servers as previously described, and plurality of branches (122 to 124). Network 120 may be connected to HO 101, which may act as a major source of information and data for several small networks (120 to 140). HO 101 may provide WAN connectivity to a corporate network or to the Internet. HO 101 may also be connected to a plurality of stand-alone branches (151, 152), which might not be part of any small network. HO 101 may provide these branches connectivity to the corporate network for example for accessing corporate data, accessing the Internet or conducting multimedia sessions with users either inside or outside the corporate network.
FIG. 1b illustrates connectivity options of a single branch 122 within a small network 120. Link 110 may illustrate connectivity of branch 122 to HQ 121, for example for accessing data servers or conducting multimedia sessions (e.g. voice and/or video) with other users of small network 120. Link 111 may illustrate WAN connectivity of branch 122 via HO 101, for example for accessing the Internet, accessing corporate data or conducting multimedia sessions with users either inside or outside the corporate network. Link 112 may illustrate connectivity of branch 122 to another branch, e.g. branch 124, which may also be part of network 120, for example for data transfer between branches or for conducting multimedia sessions between the branches. Link 113 may illustrate connectivity of HQ 121 to the corporate WAN via HO 101, for example for accessing the Internet, accessing corporate data or conducting multimedia sessions with users either inside or outside the corporate network.
In some scenarios, enterprise network 100 may be configured as a satellite based communication network, for example in order to provide connectivity between the various offices where terrestrial infrastructure is unavailable or for backup and disaster recovery purposes (e.g. after earthquakes or other disasters which may affect terrestrial infrastructure). Furthermore, in some parts of the world, lack of Internet infrastructure results in gateways to the Internet (or to any other WAN) to be located very far from the corporate facilities, in some cases even in a different continent. For example, small networks in Africa may be connected to the Internet via gateways located in Europe, where the Internet backbone is easily accessible. In such networks, using connectivity over satellite is practically the only available option. In many of these cases, these satellite communication networks may be based on demand-assignment-multiple-access (DAMA).
A DAMA satellite network may support remote terminals with ambiguous data profiles, wherein the ambiguity may be manifested by a large data rate peak to average ratio. For example, a remote terminal may be used most of the time for exchanging electronic mail messages (which may be transmitted at relatively low rate regardless of message size) or for voice connectivity, but occasionally it may be required to transmit a high rate video stream. In order to achieve efficient use of bandwidth, such networks may be designed with sufficient bandwidth to support an average network data rate, while assuming oversubscription for remote terminals' peak rates over high throughput channels. If the network is large enough (hundreds of remote terminals) utilizing a statistical approach may be justified, as normally only a small number of remote terminals require their peak rate at any given time.
When attempting to apply DAMA techniques to a small-scale satellite network (for example tens of remote terminals), wherein a considerable volume of traffic may be exchanged between remote sites, inherent limitations of the topology may lead to utilizing bandwidth less efficiently (and perhaps even to cost ineffectiveness). The low number of terminals and a higher correlation between bandwidth requests from those remote terminals may render the statistical approach unjustified, resulting in less oversubscription (i.e. more bandwidth per remote terminal). Furthermore, a relatively high volume of traffic sent from remote terminals (i.e. over return channels to a hub or to other remote terminals, e.g. in mesh topology) compared to the volume of traffic sent from a hub to remote terminals (e.g. over a forward channel) also negatively affects the bandwidth efficiency. Inbound and mesh traffic may be transmitted using bursts over return channels (e.g. in accordance with DVB-RCS recommendations), which are less efficient than a continuous, statistically multiplexed carrier as the forward channel may be (e.g. in accordance with DVB-S2 recommendations). In addition, any overhead of management and control (hardware and bandwidth) may be divided between fewer users hence the overhead per user is higher. Consequently, in terms of bits per Hz, a small-scale DAMA network may be much less efficient than a regular DAMA network.
A network topology of small-scale networks using satellite access, for example like the one illustrated for example in FIG. 1a, poses several technological challenges, including the inherent latency over satellite links, the cost of equipment and operation of a satellite network (e.g. bandwidth efficiency), operation simplicity (as operation of a satellite network may require expertise not always existing in small organizations), broadband requirements, availability requirements, user experience requirements and support of interactive applications (e.g. VoIP or video conferencing).
According to the current state of the art of satellite communication networks, several solutions and technologies exist and may be used in order to support the above described topology, in varying degree of adequacy.
A widely used solution may be a VSAT (Very Small Aperture Terminal) network in star topology, comprising a hub and plurality of remote terminals (VSATs), for example as illustrated in FIG. 8a. The hub may be configured to aggregate all the traffic to and from the remote terminals and perform all network management and control tasks. The hub may be located at a data center and/or close to an Internet backbone access point in order to provide the required connectivity to the Internet and/or intranet. In some embodiments, the outbound link (hub to remote terminals) is a point to multipoint link, based on a continuous carrier with statistical multiplexing of data frames (for example in accordance with the DVB-S2 standard recommendations) and the inbound links (from remote terminals to the hub) are point to point links, based on burst transmissions over shared bandwidth media managed using an appropriate access scheme, for example, Multi-Frequency Time Division Multiple Access (MFTDMA).
A VSAT network in star topology may be typically used in networks where the number of VSATs is measured in hundreds or more. In such systems, relatively small VSAT antennas are often used (sub-meter for Ku-band in many cases) along with a DAMA (Demand Assigned Multiple Access) satellite access scheme, which enables providing a service for a large number of users over relatively small bandwidth.
However, a VSAT network in star topology fails to meet several key requirements of the small-scale network topology previously presented. In one aspect, the bandwidth utilization efficiency expected from DAMA access schemes may be achieved only with a relatively large install base (hundreds of sites). Most SME networks may comprise only a tenth of that number of sites or even less than that. In another aspect, the star topology is efficient where almost all traffic is exchanged between the remote terminals and the data center via the hub and almost no traffic is exchanged between remote sites (e.g. branches or a second data center). Any data exchanged between VSATs travels twice via the satellite (in double hop) hence requiring approximately twice the satellite bandwidth compared to data exchanged with a data center at the hub. Since in the small-scale network topology previously presented a considerable portion of the total traffic may be exchanged between remote sites (especially between branches and their headquarters), a star topology network may be much less efficient than usually expected for such networks. In yet another aspect, any data exchanged between two VSATs is subjected to longer latency due to the additional satellite hop in each direction, hence user experience (e.g. for voice and video sessions) might be significantly compromised. In a further aspect, installing a hub for a satellite network at an SME's data center may require SME personal to operate the satellite network hence the operational simplicity requirement presented above is not satisfied as well.
In another variant of a VSAT network in star topology, a small hub may be located at each HQ of the enterprise and connectivity to the HO may be provided from each HQ via a single channel per carrier (SCPC) link. While offering efficient connectivity between branches and their HQ, the connectivity between branches and the connectivity to the Internet via the HO is in two satellite hops per direction, hence the problems of latency and user experience are not resolved but rather relocated from one link to another. In addition, the issues of bandwidth efficiency (due to network size) and operation simplicity were already presented above and are applicable in the same way to this type of solution as well.
Consequently a VSAT network in star topology, where the hub is located either at the HO or at the HQ, is an inadequate solution for a small-scale network topology as previously presented.
Another solution known in the art may be a fully meshed VSAT network, for example as illustrated in FIG. 8b. In certain networks, this topology may provide certain advantages over a star topology network, such as more efficient exchange of data between VSATs (in single satellite hop) and better user experience (lower latency). In some embodiments, as shown in FIG. 8b, a mesh network may be configured without a hub. However, such embodiments often use static channel assignments hence the total bandwidth efficiency is limited (i.e. network operation costs are higher) and the task of managing the network (e.g. adding additional sites) may be more complicated (i.e. network operation might not be simple).
However, a VSAT network in fully meshed topology fails to meet several key requirement of the small-scale network topology previously presented. In one aspect, mesh links are usually point to point links. In a topology where a VSAT may be configured to support a data center or an HQ of an SME, that VSAT may be required to concurrently maintain multiple point-to-point mesh links with plurality of other VSATs, both for transmission and reception. Since each remote terminal may be configured to have a single receiver and a single transmitter, the satellite links must be designed for aggregating the total traffic of all point-to-point links used concurrently between the data center and the other sites. This means that all VSATs in the network may be configured to transmit and receive at relatively high rate, though the throughput for each VSAT may be much lower. Achieving high throughput between remote sites (e.g. due to the above or due to broadband requirements or for video conferencing) requires a larger (and more expensive) VSAT antenna and a more powerful (and expensive) transmission equipment at each site in order to insure a sufficient link budget between any two VSATs. Consequently, the entire solution may be cost ineffective and/or face regulatory obstacles due to high transmission power. In other aspects, issues such as bandwidth efficiency (due to network size) and operation simplicity (assuming the network has a hub) were already presented above in context with the star topology network and are applicable in a similar way to this type of solution.
Consequently a VSAT network in fully meshed topology is an inadequate solution for a small-scale network topology as previously presented.
Yet another solution known in the art may be a VSAT network in a hybrid star and mesh topology, for example as illustrated in FIG. 8c, comprising a hub and plurality of remote terminals (VSATs), at least some of them configured for mesh connectivity as well as connectivity with the hub (e.g. through comprising a second inbound receiver as well as a first outbound receiver). In certain networks, a hybrid star and mesh topology may enable more efficient and lower latency connectivity between remote terminals compared to star topology.
However, a VSAT network in hybrid topology fails to meet several key requirement of the small-scale network topology previously presented. In one aspect, the issues of bandwidth efficiency (due to network size) and operation simplicity previously presented for the star topology are applicable in the same way to this type of solution. In another aspect, since the network is basically a star network and the VSATs comprise relatively small antennas and low power transmission equipment, mesh connectivity may be supported only for low throughput applications. Hence a hybrid topology may be used where the traffic between remote terminals consists for example of low-rate data transfer and/or a telephony application (which have low-rate traffic requirements), as the link rate is limited by the antenna sizes from both ends. Therefore, a hybrid topology may be inadequate for supporting a second data center at a location other than the hub, which is a key requirement in the small-scale network topology previously presented. In yet another aspect, any attempt to increase the throughput over mesh connectivity may require a larger VSAT antenna and/or a more powerful (and expensive) transmission equipment at least at one end of the mesh link. This may introduce the deficiencies of the fully meshed network, as previously presented, back into this topology.
Consequently a VSAT network in a hybrid star and mesh topology is an inadequate solution for a small-scale network topology as previously presented.
Another approach known in the art toward satellite communication networks is based on a single channel per carrier (SCPC) topology. In this approach, for example as illustrated in FIG. 8d, each link between a remote terminal and a data center requires a separate channel over a fully dedicated carrier. Those links might not be shared or multiplexed hence require permanent satellite resources, as also illustrated in FIG. 8d. 
An SCPC approach fails to meet several key requirement of the small-scale network topology previously presented. In one aspect, perhaps some of the biggest disadvantages of this approach are its inherent bandwidth inefficiency while working with non-continuous traffic (e.g. as in the case of IP networks) and its rigidness and inflexibility from satellite resources point of view. In another aspect, in a network containing more than very few sites, perhaps with one site being configured as a data center to which all the other sites may be connected and with requirements for single hop connectivity between at least some of the other sites, the necessary equipment required for implementation of such a network may be cost-ineffective, as a dedicated transceiver (transmitter and receiver) may be required for each link.
Over the years, several enhancements to the SCPC approach were introduced such as the MCPC (Multiple Channels Per Carrier) approach. Although an MCPC approach may enable time division multiplexing (TDM) of several data streams over a single carrier, this approach does not cure any of the other deficiencies previously presented with respect to the SCPC approach.
Consequently the SCPC approach is an inadequate solution for a small-scale network topology as previously presented.